The internet jokes that Valve is allergic to the number 3. However, it appears one sequel may finally reach that ever-elusive number. A recent tour of Valve's office by Reddit members has unearthed a listing for "Left 4 Dead 3."

A snapshot of an idle monitor (via Gamespot) shows a thread by a Ted Carson. "Restored L4D3," it reads, preceded by mention of Source 2--Valve's next-gen engine.

Left 4 Dead 3 previously surfaced in a supposed Valve project tracker, which also mentioned Half-Life 3. Of course, with employees being able to freely work on whatever they want, these listings won't necessarily coalesce into a real product.

Celebrating Left 4 Dead 2’s official release on Linux and America’s Day of Independence, we’re putting L4D2 on sale for a stunning 75% off and it's free to play all weekend!

We know people have a busy weekend ahead of them with BBQs, sack races, blowing fingers off, and other fun summer time activities, so we made it a little more enticing to give it a try this weekend. We are making L4D2 free to play until 10am PST Monday morning.

To all our new Linux players this weekend, Hello.

To our returning players – we are bringing back a special achievement. Good Guy Nick - – “Plays games with free weekend players and helps them survive a campaign.” Who is a free weekend player? You’re going to have to talk to each other to find out or you could always let your friends know Left 4 Dead 2 is out on Linux and is free this weekend. After all, the zombie apocalypse was made to be fought with friends.

All kidding aside, it is going to be dangerous outside this weekend. Stay indoors. Play some L4D2.

Celebrating Left 4 Dead 2 s official release on Linux and America s Day of Independence, we re putting L4D2 on sale for a stunning 75% off!

We know people have a busy weekend ahead of them with BBQs, sack races, blowing fingers off, and other fun summer time activities, so we made it a little more enticing to give it a try this weekend. We are making L4D2 free until 10am PST Monday morning.

Valve's beta version of Left 4 Dead 2 has graduated to become it plain old regular version. Yesterday's update brought the official launch of the co-op shooter's Linux version and the Extended Mutation System that lets modders create complex new modes.

The update ships with three EMS creations to show off a little what it can do, including Holdout--a neat little survival mode where you scavenge supplies to build fortifications and buy better gear. Mods with such delightful names as "Vicious Infected, Boomer Peril, Stranded, Vampirism, Plague of the Dead, Zombie Run, and Tiny Terror" are coming too, Valve says. Splendid.

The update converts L4D2 to the SteamPipe format too, for faster loading and downloads.

Like the zombies it's filled with, Left 4 Dead 2 just won't stay down. Valve continue to update their co-op FPS with new features - this time shoring up the game's Steam Workshop support with an official release of their Extended Mutations. In effect, they've mutated the mutators to provide advanced scripting tools to the community, allowing them to tweak rules and create new game modes. Like adding tiny, shrunken undead. They'd be cute if not for the biting.

Valve say they'll be highlighting some of the best mutations on the official blog later in the week. For now, they recommend Holdout: "It is a multi-map Mutation that includes the concept of resources and buildable items. It was created to showcase some of the functionality of EMS and as a byproduct, it is pretty damn fun." Valve plan to continue supporting the top community mutations through official servers.

This latest update also marks the full release of other beta features, including Linux support - which has now been rolled out to allow testing on further builds and distros. You can find the full patch notes here.

<strong>Linux</strong>
The Linux conversion is ready for primetime so we are opening it up to more people and releasing it officially on Steam. This will let us get feedback on more builds and distros.

<strong>SteamPipe</strong>
Some of you may have noticed a quick update to your game last week. That was our conversion over to SteamPipe. For L4D2 it was quick and painless as our system was already using VPKs. What does this change mean? For server operators there is an easier update path and smaller downloads. For clients, we have improved the downloading experience and you can now install L4D2 on any drive. You can get more details on <a href="https://support.steampowered.com/kb_article.php?ref=7388-QPFN-2491">the support page.</a>

<strong>Extended Mutation System.</strong>
The EMS takes the current idea of mutations and mutates it into a powerful tool for modders. They have been busy at work creating a bunch of new Mutation and game modes that will begin to be uploaded to the L4D2 workshop today. With names like Vicious Infected, Boomer Peril, Stranded, Vampirism, Plague of the Dead, Zombie Run, and Tiny Terror, there is something for everyone.

Later this week, we will highlight some of our favorites.

For now, make sure to checkout Holdout. It is a multi-map Mutation that includes the concept of resources and buildable items. It was created to showcase some of the functionality of EMS and as a byproduct, it is pretty damn fun.